Selective serotonin reuptake inhibitors (SSRI) have for years been the first choice therapeutics for the treatment of certain CNS related diseases, in particular depression, anxiety and social phobias because they are effective, well tolerated and have a favourable safety profile as compared to previously used compounds, i.e. the classical tri-cyclic compounds.
Nonetheless, therapeutic treatment using SSRI is hampered by a significant fraction of non-responders, i.e. patients who do not respond or only respond to a limited extent to the SSRI treatment. Moreover, typically an SSRI treatment does not begin to show an effect until after several weeks of treatment.
In order to circumvent some of these shortcomings of SSRI treatment, psychiatrists sometimes make use of augmentation strategies. Augmentation of antidepressants may be achieved e.g. by combination with mood stabilisers, such as lithium carbonate or triiodothyronin, or by the parallel use of electroshock.
It is known that a combination of inhibition of the serotonin transporter (SERT) with an activity on one or more serotonin receptors may be beneficial. It has previously been found that the combination of a serotonin reuptake inhibitor with a compound having 5-HT2C antagonistic or inverse agonistic effect (compounds having a negative efficacy at the 5-HT2C receptor) provides a considerable increase in the level of 5-HT (serotonin) in terminal areas, as measured in microdialysis experiments (WO 01/41701). This would imply a shorter onset of antidepressant effect in the clinic and an augmentation or potentiation of the therapeutic effect of the serotonin reuptake inhibitor (SRI).
Similarly, it has been reported that the combination of pindolol, which is a 5-HT1A partial agonist, with a serotonin reuptake inhibitor gives rise to fast onset of effect [Psych. Res., 125, 81-86, 2004].
CNS related diseases, such as e.g. depression, anxiety and schizophrenia are often co-morbid with other disorders or dysfunctionalities, such as cognitive deficits or impairment [Scand. J. Psych., 43, 239-251, 2002; Am. J. Psych., 158, 1722-1725, 2001].
Several neurotransmitters are presumed to be involved in the neuronal events regulating cognition. In particular, the cholinergic system plays a prominent role in cognition, and compounds affecting the cholinergic system are thus potentially useful for the treatment of cognitive impairment. Compounds affecting the 5-HT1A receptor and/or the 5-HT3 receptor are known to affect the cholinergic system, and they may as such be useful in the treatment of cognitive impairment.
Hence, a compound exerting 5-HT1A and/or 5-HT3 receptor activity would be expected to be useful in the treatment of cognitive impairment. A compound which moreover also exerts SERT activity would be particular useful for the treatment of cognitive impairment in depressed patients as such compound would also provide a fast onset of the treatment of the depression.
WO 03/029232 discloses e.g. the compound 1-[2-(2,4-dimethylphenyl-sulfanyl)phenyl]piperazine (example 1e) as a compound having SERT activity.